Adjustable linkage assemblies have been used for centuries to secure the position of one member pivotable with respect to another member. Such linkage assemblies allow selected rotation of one member with respect to another about an axis and, when the desired relative position of the members is obtained, enable the members to be locked in place. One of the earliest of such linkage assemblies utilizes a conventional bolt and nut mechanism, with the bolt passing through an aperture in each of the first and second members. When the desired position of the members is obtained, the nut is torqued to lock the members in their desired position. A variation of this concept is disclosed in U.S. Pat. No. 4,592,526, wherein the mating members include interlocking spline-type gears to securely lock the relative position of the members in place once the desired rotational orientation has been achieved.
A significant disadvantage of the linkage assembly disclosed in the above patent is that hand tools are required to unlock and relock the position of the members. In many applications, a linkage assembly is intended to be quickly unset, moved, and reset. In other cases, the linkage assembly preferably is controlled by various inexperienced personnel, yet must be reliably reset. In all such cases, linkage assemblies ideally do not require tooling to unlock and lock the position of one member relative to another.
U.S. Pat. No. 4,688,817 discloses a mechanism for adjusting the position of a steering handlebar with respect to a column. A lever is provided for actuating cams to lock the members in a desired position. The disclosed mechanism is complex, and in many situations sufficient space is not available for achieving the required movement of the lever. A similarly complex, lever controlled mechanism for facilitating rotation of a machine shaft is disclosed in U.S. Pat. No. 4,037,488.
Numerous other mechanisms have been designed which allow pivotable rotation of one member relative to another, while enabling the members to be selectively locked in position without tooling. U.S. Pat. No. 4,547,092 teaches a clamp with mating gear-like members which rotate relative to one another. A support rod may be connected to one of the members, and a threaded bolt with a knob head used to lock the gear-like members in their desired rotational orientation when the support rod is in its desired position. A relatively simple position retaining mechanism is disclosed in U.S. Pat. No. 4,620,813, Duel toothed arcs are hinged together in opposition, and are maintained in position by a biasing spring, with each of the arcs being adapted for mating engagement with corresponding teeth on the exterior surface of a shaft. In operation, the handles of the two arcs are pressed together against the spring bias force to cause separation and allow decoupling and rotation of one member relative to another. Thereafter, the handles are released and the toothed arcs again mated to the shaft to lock the position of the members in place. An articulated linkage system is disclosed in U.S. Pat. No. 4,447,170. This mechanism includes L-shaped brackets, each having a spring loaded release mechanism. A button may be actuated to allow rotation of one bracket relative to another, and thereafter released to lock the position of the brackets in place.
The above mechanisms have one or more disadvantages which have induced the redesign of a gimbal joint according to the present invention. As previously noted, many such linkage mechanisms are large or require a great deal of space for operation, and according cannot be used in compact assemblies or in locations where space is a premium. Some device are comparatively complex and thus costly, while other devices are simple but lack the desired strength to lock the members in their desired position. Most prior art devices either require special tooling, or can be inadvertently actuated to allow movement of one member relative to another when not intended, thereby creating a safety risk.
A further disadvantage of many prior art adjustable linkage assemblies is that the torque which may be transmitted through the locked linkage assembly and between the first and second members depends on operator discretion, thereby reducing reliability. In other linkage designs, forces are not uniformly transmitted between assembly components, so that the interlocking components must be oversized. Other linkage assemblies are not easily utilized by increasingly popular robotically controlled arms. Improved linkage assemblies are required, for example, in outer space applications where near-zero gravity conditions create additional manipulation problems when such linkage assemblies are operated by either personnel or computer controlled equipment.
The disadvantages of the prior art are overcome by the present invention. An improved linkage assembly is hereinafter disclosed for selectively retaining the position of one member rotatable about an axis with respect to another member. The linkage assembly of this invention is relatively simple in construction, compact, and has superior locking strength. A gimbal joint of the present invention may be quickly and easily used without special tooling by inexperienced personnel or computer controlled equipment, and is designed to prevent inadvertent actuation.